Muscle stimulating device and method for diagnosing and treating a breathing disorder

ABSTRACT

A device and method for magnetic stimulation of muscles for the diagnosis and relief of a breathing disorder, such as obstructive sleep apnea. Magnetic stimulation is used to stimulate muscles which serve to stabilize the upper airway of an individual whose nocturnal apneic events are related to diminished muscle tone. A sensor monitors a physiologic characteristic of the patient, a coil is energized to stimulate the appropriate muscles associated with the upper airway, a power supply provides power for energizing the coil, and a control system controls the application of power to the coil based on the output of the sensor. Diagnosis of obstructive sleep apnea is accomplished by measuring the subject&#39;s compliance in the presence and absence of the magnetic stimulation of the upper airway muscles. The smaller the difference between these two compliance levels, the more likely that patient suffers from obstructive sleep apnea.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention pertains to an apparatus and method fornoninvasive stimulation of muscles in the upper airway to diagnoseand/or treat a breathing disorder, such as obstructive sleep apnea. Inparticular, the present invention pertains to a magnetic stimulationdevice and a method of using the device to apply pulsed magnetic fieldsto the muscles in the neck area of a patient to induce tension in suchmuscles, thereby relieving the obstructive sleep apnea caused by arelaxation of such muscles. By measuring an awake patient's compliancein the presence and absence of the magnetic stimulation, the likelihoodthat the patient suffers from obstructive sleep apnea can be determined.

[0003] 2. Description of the Related Art

[0004] Obstructive sleep apnea (OSA) is a condition in which sleep isrepeatedly interrupted by an inability to breathe due to an obstructedupper airway segment. Those afflicted with OSA experience sleepfragmentation and complete or nearly complete cessation of ventilationintermittently during sleep with potentially severe degrees ofoxyhemoglobin desaturation. These symptoms may be translated clinicallyinto extreme daytime sleepiness, cardiac arrhythmias, pulmonary-arteryhypertension, congestive heart failure and/or cognitive dysfunction.Other consequences of OSA include right ventricular dysfunction, carbondioxide retention during wakefulness, as well as during sleep, andcontinuous reduced arterial oxygen tension. Hypersomnolent sleep apneapatients may be at risk for excessive mortality from these factors aswell as by an elevated risk for accidents while driving and/or operatingpotentially dangerous equipment.

[0005] Studies of the mechanism of collapse of the airway suggest thatduring some stages of sleep, there is a general relaxation of themuscles which stabilize the upper airway segment. This generalrelaxation of the muscles is believed to be a factor contributing toOSA.

[0006] Existing therapeutic remedies for treating OSA include thesurgical removal of deformed, loose or swollen structures in the upperairway. It is also known to apply positive air pressure at the mouthand/or nose of the patient to “splint” the airway, thereby maintainingan open passage to the lungs. In addition, pharmacologic solutions havealso been pursued.

[0007] Neither of these therapies is successful in all cases. Surgicalrelief is invasive, introduces a potential for surgical complicationsand is appropriate in only a small percentage of cases. On the otherhand, the nasal mask needed to apply a positive air pressure is nottolerated by some OSA patients. Pharmacological therapy has been, ingeneral, less than satisfactory, and side effects are frequent.

[0008] It is also known to treat OSA by electrically stimulating themusculature in the neck area associated with the upper airway. One suchmethod of electrically stimulating the muscles in the upper airway areaof a patient involves placing an electrode in direct contact with asurface of the patient and passing a current through the surface tissuesof the patient contacting the electrode. For example, an intraoralappliance has been developed that applies electrical currents to thetongue, causing it to contract, thereby helping to clear the airway.Another known appliance applies electrical stimulation to the exteriorsurface of the patient's neck below the chin to induce contraction ofthe upper airway muscles.

[0009] Electrical stimulation using surface mounted electrodes createsrelatively large current densities at the site of the electrodes.Because these current densities are disposed at the surface of thepatient, which also contains a relatively large number of nerve endings,such electrical stimulation devices can cause unpleasant or painfulsensations, possibly arousing the user from sleep.

[0010] It is also known to apply electrical stimulation to the musclesof the upper airway via electrodes implanted in the patient.Subcutaneous electrodes have the benefit of being positioned adjacent tothe muscle or nerve to be stimulated to focus the electrical energy onthat muscle/nerve while reducing the amount of collateral tissueseffected by the high current densities near the electrode. There arealso typically fewer nerve endings deep within the patient than at thesurface. Thus, electrical stimulation using implanted electrodes reducesthe likelihood that the electrical stimulation will induce an unpleasantor painful sensation in the patient. However, electrical musclestimulation utilizing implanted electrodes requires surgicalintervention, the permanent presence of foreign materials within thepatient's neck tissue, and at least one electrical connection protrudingfrom the patient. Consequently, there is a potential for infection orirritation at the surgical site and at the site where the electrodeprotrudes through the surface of the patient.

SUMMARY OF THE INVENTION

[0011] Accordingly, it is an object of the present invention to providea device for stimulating the muscles in the upper airway area for thetreatment of OSA that does not suffer from the disadvantages associatedwith the above-described conventional OSA treatments. This object isachieved by providing a non-invasive device for magnetically stimulatingthe muscles that stabilize the upper airway to cause them to contract.Because the stimulation is via magnetic induction, which is capable ofstimulation of deep muscular structures, the present invention does notgenerate large currents at the skin. Therefore, it is less painful thansurface electrode electrical stimulation devices.

[0012] The muscle stimulator for applying a magnetic field to at leastone muscle or muscle group associated with an upper airway in a patientexperiencing obstructive sleep apnea to induce tension in that muscle ormuscle group to relieve the obstructive sleep apnea includes a pluralityof loops of electrical wire and a power supply that selectively provideselectrical power to the plurality of loops. Applying power to the loopsproduces the magnetic field used to stimulate the targeted muscles. Asensor monitors a condition of the patient associated with theobstructive sleep apnea, such as the snoring sounds produced by thepatient or the patient's respiration, to determine when to initiatestimulation and how to change the intensity of the stimulation, ifnecessary, during the therapy process. A control unit receives signalsoutput by the sensor and controls the application of electrical powerfrom the power supply to the plurality of loops of electrical wire. Apositioning appliance secures the plurality of loops of electrical wireto the patient at a position relative to the targeted muscle or musclegroup such that the magnetic field produced by applying electrical powerto the plurality of loops of electrical wire induces tension in thatmuscle or muscle group to relieve the obstructive sleep apnea.

[0013] It is a further object of the present invention to minimize theheat experienced by the patient as a result of using the magneticstimulator. To that end, the present invention includes an insulatingmaterial between the patient's skin and the coil. In addition, thetemperature of the coil is monitored by a temperature sensor and thepower to the coil is controlled based on the temperature of the coil sothat excessive heat is not generated in the coil. Also, portions of thecoil are maintained as far from the patient as possible while stillpermitting the magnetic stimulator to provide its therapeutic effect.

[0014] It is a still further object of the present invention to controlthe application of magnetic energy to the patient based on the conditionof the patient. To achieve this object, sensors are provided to monitorthe condition of the patient. For example, sensors are used to determinewhether the patient is snoring and/or experiencing an apneic event. Ifso, the coil is energized to treat the OSA. Energizing the coil can alsobe synchronized with the patient's respiration so that stimulationbegins within a predetermined window during the patient's respiratorycycle, such as at the onset of inspiration or at a period offsettherefrom. Also, the present invention contemplates using the conditionsof the patient, such as the presence of snoring, an apneic event and/orthe respiratory patterns of the patient, to regulate the intensity ofthe magnetic stimulation. For example, the more prevalent the apneicevents, the greater the level of stimulation. Conversely, a reducednumber of apneic events results in a reduced level of stimulation. Inthis manner, only the necessary level of magnetic energy is applied tothe patient.

[0015] It is a further object of the present invention to provide amethod of using the device discussed above to apply a magnetic field toat least one muscle group associated with an upper airway of a patientexperiencing obstructive sleep apnea to induce tension in that musclegroup to treat the obstructive sleep apnea.

[0016] It is yet another object of the present invention to provide asystem and method for diagnosing whether a patient is likely to sufferfrom OSA. This object is achieved by providing a system that measures acompliance of the patient to obtain a first compliance level, applies amagnetic field to at least one muscle group associated with an upperairway of the patient, measures the compliance while applying themagnetic field to obtain a second compliance level, and compares thefirst compliance level to the second compliance level. The smaller thedifference between the first and second compliance levels, the morelikely the subject suffers from obstructive sleep apnea.

[0017] These and other objects, features and characteristics of thepresent invention, as well as the methods of operation and functions ofthe related elements of structure and the combination of parts andeconomies of manufacture, will become more apparent upon considerationof the following description and the appended claims with reference tothe accompanying drawings, all of which form a part of thisspecification, wherein like reference numerals designate correspondingparts in the various figures. It is to be expressly understood, however,that the drawings are for the purpose of illustration and descriptiononly and are not intended as a definition of the limits of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a perspective view of a magnetic stimulator according tothe principles of the present invention;

[0019]FIG. 2 is a side view of a person wearing the collar illustratedin FIG. 1;

[0020]FIG. 3 is another side view, partially in section, showing ingreater detail the collar of FIG. 1 positioned on the patient;

[0021]FIG. 4 is a plan view of a first embodiment of the coil disposedin the collar portion of the magnetic stimulator;

[0022]FIG. 5 is a front view illustrating the superposition of the coilillustrated in FIG. 4 with respect to the neck of the patient;

[0023]FIG. 6 is a side view of the coil structure illustrated in FIG. 4showing the positioning of the coil relative to the patient's neck;

[0024]FIGS. 7A, 7B and 7C illustrate a second, third and fourthembodiment, respectively, for the coil in the collar portion of themagnetic stimulator;

[0025]FIGS. 8A and 8B illustrate a fifth embodiment for the coil in thecollar;

[0026]FIG. 9 illustrates an alternative embodiment for the collar;

[0027]FIG. 10 is a schematic diagram of the magnetic stimulatorillustrated in FIG. 1;

[0028]FIG. 11 is a flowchart illustrating a process carried by themagnetic stimulator in achieving its therapeutic effect;

[0029]FIG. 12 is a side view of the coil, a portion of the patient'sneck, and a miniature intramuscular stimulator according to anotherembodiment of the present invention;

[0030]FIG. 13 is a schematic diagram of the miniature intramuscularstimulator adapted for use with the magnetic stimulator of the presentinvention; and

[0031]FIG. 14 is a schematic diagram of a system for diagnosing whethera patient is likely to suffer from OSA using the magnetic stimulator.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS OF THEINVENTION

[0032]FIG. 1 illustrates a first embodiment of a magnetic stimulator 30according to the principles of the present invention. Magneticstimulator 30 includes a control unit 32 and a collar 34 coupled tocontrol unit 32 via a flexible cable 36. Collar 34 attaches to thepatient's neck, as shown in FIG. 2, such that a portion 35 of collar 34containing at least one magnetic field generating coil is disposeddirectly under the patient's chin 37. Control unit 32 receives signalsfrom at least one sensor, such as sensor 38, which is connected tocontrol unit 32 via a cable 39. Control unit 32 energizes the coil incollar 34 to produce a time varying electrical current that creates achanging magnetic field, whose rapidly increasing flux, in turn, createsa spacially varying electric field having a gradient that is maximizedat specific muscles and/or muscle nerves in the upper airway. In short,the changing magnetic field produced by energizing the coil with a timevarying current, such as a pulse train, induces tension in the musclespulling the obstructing tissue from the patient's airway, therebyrelieving the obstructive sleep apnea.

[0033] In the embodiment illustrated in FIG. 1, power is provided tocontrol unit 32 from an external power supply. It is to be understood,however, that batteries or other internal power storage devices can beprovided in place of, or in addition to, the external power source toenergize the coil in collar 34, sensor 38, and/or the components withincontrol unit 32.

[0034] In the illustrated embodiment, control unit 32 includes manuallyoperable actuating mechanisms 33, such as buttons, dials, knobs orswitches, for performing functions such as activating and deactivatingthe unit, setting the ranges for the output field strength and/orduration, setting threshold values, setting operating modes, andconducting diagnostic routines on the magnetic stimulator. The presentinvention also contemplates that one control unit can be used inconjunction with a plurality of sensors, a plurality of collars, and/ora plurality of collar-sensor combinations. If one control unit is beingused in conjunction with a plurality of sensors, a plurality of collars,and/or a plurality of collar-sensor combinations, that control unitwould include additional input/output interfaces 31 a for connecting theadditional sensors, collars, and or collar-sensor combinations thereto.

[0035] The control unit can also be configured with any appropriateinput/output interface for exchanging data between the control unit andan external source. For example, one or more interfaces 31 b can beprovided for accessing, modifying, or downloading data stored in thecontrol unit. Such data exchange interfaces can include, but are notlimited to, an RS-232 port, modem, coaxial, optical fiber, rf, infrared,ultrasonic, or other interfaces that permit data exchange between thecontrol unit and the external device. For example, data can be providedto the control unit using manual input devices, such as knobs, switches,buttons, and/or keypads coupled to or integral with the control unit.Data can also be provided to, modified or extracted from the controlunit using an external computer that communicates with the control unitusing an appropriate interface.

[0036] In the illustrated embodiment, control unit 32 and collar 34include warning devices, such as an audio indicator 41 a and a visualindicator 41 b, that inform the user, or a person monitoring the user,of the condition of the patient and/or magnetic stimulator 30. Forexample, an audio or visual warning can be generated if the patient hasstopped breathing for a predetermined period of time, has begun or hasstopped snoring, and/or has removed or put on the collar. Of course, anappropriate sensor or plurality of sensors for sensing such conditionsmust be provided.

[0037] As noted above, the present invention also contemplates providingwarning signals indicative of the status of the magnetic stimulator. Forexample, an audio or visual warning signal can be generated if the coilin the collar exceeds a predetermined temperature, if the power providedto the control unit, the sensors, or the collar has been shut off, fallsbelow a predetermined level or exceeds a predetermined level, if thesensors or the coil are not working, have become disconnected or fail tocommunicate with the control unit, and/or if there is a short in thecoil, sensors and/or control unit.

[0038] In addition to or in place of the relatively simple audio/visualwarning indicators 41 a and 41 b, other warning devices can be provided.For example, control unit 32 can include circuitry for notifying aremotely located third party of the existence of the condition causingthe warning, using, for example, signals communicated via telephonelines. Furthermore, the warning signals, as well as other signalsindicative of the condition of the patient and/or the magneticstimulator that do not constitute a warning, can be provided to adisplay device (not shown) such as a monitor or LED. Such a displaysystem may be particularly beneficial in a sleep lab setting where asingle control unit is being used to monitor and magnetically stimulatea plurality of patients under the supervision of a sleep lab technician.

[0039] It is to be further understood, that the collar, control unit andsensors need not be separate elements. For example, as discussed ingreater detail below, the sensor can be disposed on the collar so thatthe collar-sensor combination functions as a unit. In addition, thecontrol unit can also be provided on the collar so that most of thecomponents of the magnetic stimulation system, i.e., the sensors, coil,and control unit are contained in one assembly that is worn by thepatient. Depending on the power requirements, the power supply can alsobe provided in that assembly, further minimizing the number ofcomponents that the patient has to be concerned with when using themagnetic stimulator.

[0040] As shown in FIG. 3, which is a schematic illustration of themuscles associated with the upper airway, the muscles targeted forstimulation are the geniohyoid muscle 40 under the chin 37, the left andright sternohyoid muscles 42, the left and right thyrohyoid muscles 44,and the left and right sternothyroid muscles 46. The sternothyroid,sternohyoid and thyrohyoid muscles are arrayed in pairs on either sideof the trachea mid-line. However, for ease of illustration, only one ofeach of these muscles is illustrated in FIG. 3, which also shows therespective attachments of these muscles to the sternum 48, mandible 50,thyroid cartilage 52 and hyoid arch 54.

[0041] These muscles have been identified by the present inventors asbeing particularly relevant to the onset and prevention of OSA because,when contracted, these muscles brace the hyoid arch and increase tensionin the tissue surrounding the upper airway, thereby preventingobstruction of the airway. It has been discovered that during sleep, insome patients, the relaxation of these muscles decreases the hyoid archsupport and the support of the tissue surrounding the upper airway to anextent sufficient to result in obstruction of the upper airway, therebycausing those patients to suffer from OSA. The present invention avoidsthis consequence by magnetically stimulating the geniohyoid,sternothyroid, sternohyoid and thyrohyoid muscles so that they providethe proper level of support even while the patient is asleep.

[0042] It is to be understood that while the geniohyoid, sternothyroid,sternohyoid and thyrohyoid muscles are the primary muscles that thepresent invention contemplates stimulating, this invention is notlimited to stimulation of these particular muscles. Other muscles ormuscle groups, instead of or in addition to these muscles, can betargeted for stimulation. For example, the genioglossus, the stylohyoidmuscle and hyoglossus muscle attaching to the rostral surface of thehyoid cartilage, and the omohyoid muscle, which attaches below the hyoidcartilage, are possible targets for stimulation, so long as any suchstimulation furthers the goal of supporting the tissues surrounding theupper airway to reduce and/or minimize the occurrence of OSA.

[0043] As shown in FIG. 3, when properly worn by the patient, collar 34positions a coil 56 in an overlying relationship with the geniohyoid,sternothyroid, sternohyoid and thyrohyoid muscles so that the magneticfield generated by passing a current through coil 56 is specificallytargeted on these muscles and/or on the nerves controlling thecontraction of these muscles. Collar 34 encircles the patient's neck andis made from a comfortable, semi-flexible material. Collar 34 must beflexible enough to be fitted on and comfortably worn by the patient.However, it must be rigid enough to maintain coil 56 in an appropriateposition relative to the targeted muscles so that at a localizedconcentration of the magnetic field occurs at these muscles even if thepatient moves during sleep. The collar is also preferably made from aheat insulating material so that heat generated by the current passingthrough the coil is prevented from reaching the patient. To furtherachieve this goal, an additional thermo-insulating material or layers ofsuch material can be provided between coil 56 and the inside surface ofcollar 34.

[0044] It is to be understood that the present invention is not limitedto the illustrated configuration of the collar. Quite the contrary, thepresent invention contemplates any positioning device that locates andmaintains the coil in an appropriate position to stimulate the targetedmuscles while minimizing heat transfer to the patient. For example, thepresent invention contemplates that coil 56 can be attached to thepatient using an adhesive, for example, without the need for a collar.In which case, an insulating material can be provided between the coiland the patient that is also attached to the patient using any suitablemethod, such as adhesive.

[0045] In one embodiment of the present invention, magnetic stimulator30 is dynamically controlled so that stimulation is only applied to thepatient's upper airway muscles as required in order to counteract theoccurrence of OSA. For this reason, sensors, such as sensor 38 in FIG.1, are provided to detect the onset of OSA by monitoring characteristicsof the patient indicative of this event. It is to be understood,however, that other characteristics of a patient that may or may notrelate to the onset of OSA, such as body temperature, can be monitoredby the sensors and the control unit of this invention to provide moregeneral information on the condition of the patient, which may be usefulin determining the condition of the patient throughout the stimulationprocess. This information may be particularly useful in the sleep labsituation or hospital. Another patient characteristic that can bemonitored is the blood gas levels, such as the oxygen and/or CO₂ levels.Blood gas information can be used to monitor the effectiveness of thestimulation or to control the activation and/or deactivation of suchstimulation.

[0046] In one embodiment of the present invention, sensor 38 is anacoustic sensor that is positioned near or on the patient to sense theonset of inspiration-induced upper airway collapse, which manifests inthe form of snoring sounds emitted by the patient. Such snoring soundsare typically produced by the unstable airway vibrating duringinspiration, and the occurrence of a snore and its increase inprominence in successive breaths can indicate the onset of an apneicevent. The increase in snore intensity on successive inspirations warnsof the impending need for magnetic stimulation on a subsequentinspiration. Thus, detecting the occurrence of a snore and controllingthe stimulator based thereon is an effective method for dynamicallycontrolling stimulation so that it is only applied to the patient asnecessary to counteract the occurrence of OSA.

[0047] In another embodiment of the present invention, one or moresensors are provided to detect the respiratory patterns of the patient.This can be accomplished, for example, by monitoring the airflow in thepatient's airway and/or the expansion and contraction of the chest,thorax and/or abdomen. The magnetic stimulator can be activated during aspecific window in the patient's respiratory cycle, such as at the onsetof inspiration or at a period offset therefrom, to prevent or threatOSA. The present invention also contemplates monitoring the patient'sEMG activity and stimulating the patient based thereon.

[0048] In the embodiment illustrated in FIG. 1, sensor 38 is a separatecomponent from collar 34. As such, it must be separately mounted on thepatient. This configuration is advantageous in that it permits one ormore sensors to be located at various spaced apart locations on thepatient unrelated to the other elements of the magnetic stimulator, suchas the collar, for monitoring the same or different conditions of thepatient from various anatomical locations. For example, the patient'sheart rate can be monitored from sensors located on the front and backof the patient's torso.

[0049] It has been determined through clinical testing that the soundfrequencies that correspond to upper airway narrowing are in the rangeof 20-250 Hz. To optimize the detection of upper airway sounds in thisbandwidth, it is preferable to locate an acoustic sensor on the externalsurface of the patient's throat. In the embodiment illustrated in FIG.3, an acoustic sensor 58 is fixed at the inside surface of collar 34 sothat sensor 58 is positioned at the external surface of the patient'sthroat when collar 34 is worn by the patient. This configuration alsoenables both the coil and the sensor to be properly mounted on thepatient by merely donning collar 34, thereby avoiding the need to placethe collar and sensor on the patient separately. Sensor 58 is coupled tocontrol unit 32 via wiring 60 and transmits a signal indicative of thesounds generated in the patient's upper airways to the control unit.

[0050] While the sensor described above detects throat vibration usingan acoustic sensor, it is to be understood that other sensors capable ofdetecting the onset of an upper airway event are within the scope of thepresent invention. Examples of other suitable sensors include airflowsensors, pressure sensors, an electromyogram (EMG) as a measure ofmuscular effort, and fiber-optic vibration sensors. Such sensors can beoperatively coupled to the collar, the control unit or can be wireless.Furthermore, while only one patient condition monitoring sensor isillustrated in collar 34 of FIG. 3, other sensors in addition to or inplace of sensor 58 can be provided at the same locations or at otherlocations than that illustrated in FIG. 3. For example, an acousticsensor may be provided on an exposed surface of collar 34 instead of orin addition to audio sensor 58. Also, a pressure sensor and/or an EMGsensor, separate from collar 34, may be fixed to the patient formonitoring inspiration or muscle effort, respectively. The data from thecombination of sensors can be compared and analyzed together to detectmore accurately the onset of an upper airway event that is indicative ofthe occurrence of OSA.

[0051] Collar 34 in FIG. 3 also includes a second sensor 62 in the formof a thermistor probe to monitor the temperature of coil 56. Sensor 62enables the control unit to prevent electrical energy from beingprovided to coil 56 in the event the heat generated by energizing thecoil exceeds a predetermined threshold. Sensor 62 is connected to thecontrol unit via electrical wiring 64 within the collar. Electricalwiring 60 and 64, as well as the electrical wiring providing power tocoil 56, can be provided in the same flexible tube 36 so that only onecable and one interface are needed between the collar and the controlunit.

[0052] In the embodiment illustrated in FIG. 3, cable 36 connects coil56 to a power supply. It is to be understood, however, that othermethods of providing power to coil 56 are contemplated by the presentinvention. For example, collar 34 can contain an internal power supplyfor energizing coil 56, thus eliminating the need for a dedicated powersupply line between the control unit and the coil. Such a configurationrequires a communication link between the control unit and the powersupply system in the collar so that activation, deactivation and energylevels provided to the coil can be controlled. Such a communication linkcan be hardwired or wireless.

[0053] It is to be further understood that the data link between thecontrol unit and sensors 58 and 62 can be hardwired, as shown in FIG. 3,or wireless, so long as data is transmitted by the sensors to thecontrol unit. Wireless communication, which can be rf, infrared, orultrasonic, for example, requires that a power supply be provided oncollar 34 for powering sensors 58 and 62. Furthermore, data can be sentfrom sensors 58 and 62 automatically, for example at regular timedintervals, or upon a request from the control unit. This lattertechnique, however, requires that sensors 58 and 62 have the ability toreceive and process commands from the control unit and that the controlunit have the ability to transmit and process these commands and theassociated responses.

[0054] Details of a first embodiment of coil 56 and the general positionof coil 56 relative to the patient are discussed below with reference toFIGS. 4-6. As shown in FIG. 4, coil 56 includes a plurality ofadjacently located loops, identified 1, 2, 3, and 4. Loops 14 each haveone or more turns, and the entire coil is wound from a continuous lengthof electrical wire, such as copper or silver, so that only one pair ofterminals 73 are needed to energize all four loops. An electricalinsulation separates each turn in each loop from the other turns in thatloop. Each loop can be configured so that the wires in each turn of thatloop lie in the same plane, as shown in FIG. 4. However, otherconfigurations for the wires in the loops are possible. For example, theturns in a loop can be stacked one on another, or twisted or braidedtogether.

[0055] The structure of coil 56 and the direction of current flowthrough the loops, as shown by the arrows in FIG. 4, is selected tooptimize the magnetic field intensity at certain locations relative tocoil 56. In particular, increased magnetic field intensities are createdin an area below coil 56 corresponding to areas A, B, C, and D betweenadjacent loops at which currents summate. In other words, an area ofincreased magnetic field strength is created in an area below the coilwhere two loops are adjacent one another and where the currents flowthrough these adjacent loops in the same direction. In FIG. 4, thecurrents in loops 1 and 2 at area A are flowing in the same direction,e.g., downward relative to the top of this diagram. Thus, there is anarea of increased magnetic field strength in a region below coil 56,i.e., in a direction toward the page, corresponding to area A. Thisincreased magnetic field strength is caused by a summation of magneticfields generated by loops 1 and 2. Similar areas of increased magneticfields are created at areas corresponding to areas B, C, and D.

[0056] In the embodiment illustrated in FIG. 4, four areas of increasedmagnetic field strength are created in order to target the stimulatingeffect provided by the present invention at four regions of thepatient's neck. These regions correspond to the locations of thegeniohyoid 40, sternothyroid 46, sternohyoid 42 and thyrohyoid 44muscles. See FIG. 5. By providing the specific configuration for coil56, the present invention stimulates only muscles deemed to beparticularly suited to maintaining an unobstructed airway.

[0057] In the embodiment of the present invention illustrated in FIG. 3,in which sensors 58 and 62 are provided on or in collar 34, it isdesirable to locate these sensors in an area where the magnetic fieldintensity is at a minimum. Such an area is identified as area E in FIG.4 and corresponds to a position between adjacent loops 2 and 3 where thecurrent in each loop are flowing in opposite directions.

[0058] While FIGS. 4-5 suggest that loops 1-4 lie in the same plane,other configurations for loops 14 are contemplated by the presentinvention. For example, as shown in FIG. 6, it is desirable to orientloops 2 and 3 in separate planes so that the area of increased magneticfield strength created at the area between loops 1 and 2 and betweenloops 2 and 4 is targeted toward geniohyoid muscle 40 when the collar ispositioned on the patient. Similarly, the area of increased magneticfield strength created at the area between loops 1 and 3 and betweenloops 3 and 4 is targeted toward the sternothyroid 46, sternohyoid 42and thyrohyoid 44 muscles. Thus, loop 2 and the upper portions of loops1 and 4 adjacent to loop 2 are generally parallel the surface of theneck under the patient's chin 37, while loop 3 and the lower portions ofloops 1 and 4 adjacent to loop 3 are generally parallel to the portion72 of the patient's neck between chin 37 and the sternum when the collaris worn by the patient. Please note that FIG. 6 does not illustrateportions of the collar, other than coil 56, for ease of illustration.

[0059] Because energizing coil 56 tends to cause heating of the coil, itis also desirable to position portions 74 and 76 of loops 1 and 4,respectively, which are not adjacent loops 2 and 3, as far as possiblefrom the surface of the patient. Increasing the distance from portions74 and 76 of loops 1 and 4 to the surface of the patient maximizes thethermal protection afforded by the collar, so that as little heat aspossible is transferred to the patient. In addition, locating portions74 and 76 of loops 1 and 4 as far as possible from the patient's skinminimizes the possibility of unwanted stimulation of nerves, such as thephrenic nerve, which contracts the diaphragm, and the vagus nerve, whichdepresses the patient's heart rate, by the magnetic fields generated bythe coil. The configuration of the coil concentrates the magnetic fieldsin the areas shown in FIG. 4. At all other areas, the field strength isminimized so that the only significant stimulation takes place at thetargeted locations.

[0060] A second embodiment for the coil used in the collar according tothe principles of the present invention is shown in FIG. 7A. In thisembodiment, six generally similar loops 82, 84, 86, 88, 90 and 92 definecoil 80 with a current passing therethrough as indicated by the arrows.In the illustrated embodiment, loops 82, 84, 86, 88, 90 and 92 have thesame number of turns and are wound from a continuous electrical wire.Because the loops in coil 80 are connected in series, a single pair ofterminals 94 are all that is required to energize the coil. The coilconfiguration illustrated in FIG. 7A provides generally the samemagnetic field pattern as the coil configuration illustrated in FIGS.4-6. Namely, four magnetic field concentrations of generally uniformmagnitudes are provided generally at areas A, B, C and D when a currentis provided to terminal 94.

[0061] As noted above, the plurality of loops in coil 56 of FIG. 4 andin coil 80 of FIG. 7A are defined from a continuous wire so that onlyone pair of leads is connected to the power supply. The same currentflows through each loop. It is to be understood, however, that it is notnecessary for each loop in the overall coil to be connected to any otherloop. For example, in an alternative embodiment of the present inventionillustrated in FIG. 7B, coil 81 is defined by six loops separated intotwo groups of loops 83 a-83 c and 85 a-85 c, wherein each group of loopsis made from a continuous length of wire and is energized by anindependent power supply.

[0062] As with the previous embodiments, four areas of increasedmagnetic field concentrations A-D are created by energizing loops 83a-83 c and 85 a-85 c. Loops 83 a, 83 b and 83 c have a common terminal87, and loops 85 a, 85 b and 85 c have a common terminal 89. As notedabove, terminals 87 and 89 can be connected to separate power supplies,i.e., driven by separate currents, so that each group of loops isenergized independently of the other, both in terms of timing andmagnitude. Alternatively, terminals 87 and 89 can be connected togetherso that each group of loops receives the same current. This thirdembodiment of the coil simplifies the manufacture of the coil byenabling each group of loops to be made individually and combined todefine the coil, thereby avoiding the relatively complicated windingpattern required to manufacture the coil illustrated in FIGS. 4 and 7A.

[0063]FIG. 7C illustrates a fourth embodiment in which each loop 93 a-93f in coil 91 is independent of the other loops in that coil so that eachloop 93 a-93 f has its own terminal 95 a-95 f, respectively. Becauseeach loop is capable of being energized individually, this configurationmaximizes the variety of patterns of increased areas of magneticstimulation that can be created by coil 91, the intensity of thestimulation at each area, and the timing at which these areas arestimulated, all of which is done under the control of the control unit.

[0064] It is to be understood that each loop need not have the samenumber of turns or be energized at the same voltage/current or at thesame time as the other loops or other groups of loops. Instead, thedesired magnetic field pattern can be selected by adjusting theseparameters so that specific muscles are targeted for stimulation and arestimulated at a specified timing. For example, if there is an area thatshould be stimulated with a larger intensity than the other areas, thenumber of turns in the loops associated with that area can be increased,with the current level being kept constant, or the current level to theloops associated with that area can be increased, with the currentlevels provided to the other loops remaining unchanged. If there is anarea that is to be stimulated before the other areas, current can beprovided to the loops or group of loops associated with that area priorto being provided to the other loops. If groups of loops are provided,rather than individual loops, the groups of loops can be powered atdifferent levels by associated power supplies, have numbers of turnsthat are different from other groups of loops, and/or configurationsthat are different from other groups of loops, and be energized attimings different from the other groups of loops to achieve a variety ofmagnetic field intensities, patterns and timings.

[0065] For example, the coil structure in FIG. 4 can be modified so thatloops 1 and 4 are energized together and so that loops 2 and 3 areenergized independently of one another. This configuration permits loops1, 2 and 4 to be energized as a group to stimulate areas A and B.Similarly loops 1, 3, and 4 can be energized as a group to stimulateareas C and D. Also, the timing at which each areas A-D are stimulatedcan be synchronized or independent so that one area or more areas arestimulated at the same time, at an offset time period or at differenttimes than the other areas.

[0066] It can be appreciated that a wide variety of loop configurations,activation combinations or patterns, activation timings and stimulationintensities can be provided so that a single coil structure, such asthose shown in FIGS. 4-7C, can provide many different magnetic fieldpatterns. The different magnetic field patterns can be created byindependently modulating the electrical current magnitude, phase, andduration, in each loop or groups of loops in the coil. The control unitis used to set the energizing pattern, magnitude and timing for the coilso that selected loops are activated at selected power levels atappropriate times to produce a particular magnetic field pattern with aparticular stimulation intensity at selected portions of that pattern.Ideally, the magnetic field pattern, stimulation intensities andstimulation timing targets the muscles in the patient that maximize theOSA treatment capabilities of the present invention.

[0067] A fifth embodiment of the coil is shown in FIGS. 8A-8B. In thisembodiment, coil 106 is defined by three adjacent loops 108, 110 and 112with the current flowing therethrough as illustrated by the arrows. Thisconfiguration provides two areas 114 and 116 of concentrated magneticstimulation. However, this configuration is more compact than the coilconfigurations of the previous embodiments. As shown in FIG. 8B, ends118 and 120 of outer loops 108 and 112 are spaced apart from a surface122 of the patient to minimize heat transfer to the patient and preventthe magnetic fields from stimulating the phrenic and/or vagus nerves.

[0068] As with the previous embodiments, the loops shown in FIGS. 8A and8B can be wound as a group of individually so that each loop isindependent of the other loops. Also, the loops can be energizedtogether from a common source, in groups, or individually and can beenergized at the same or different power levels and at the same time orat different times depending on the desired magnetic field pattern.

[0069]FIG. 8C illustrates a sixth embodiment for the coil. Coil 111 inthis figure is similar to the coil configuration shown in FIGS. 4-6except that one of the large loops have been deleted, leaving athree-loop coil with two areas 113 of field strength summation. Thiscoil configuration is advantageous in that is reduces the coilresistance and inductance as compared to the coil of FIGS. 4-6.

[0070] It is to be understood that loop shapes, other than those shownin FIGS. 4, 7A-7C and 8A-8C are contemplated by the present invention.For example, one or more of the loops in the same coil can be circular,elliptical, square, triangular, or rectangular. Also, the presentinvention contemplates providing more than one coil in the collar. Eachsuch coil can have an overall shape, loop configuration, power supply,and activation pattern (including activation timings and intensity) thatdiffers from the other coils in the collar.

[0071]FIG. 9 illustrates a second embodiment for the collar. In thisembodiment, collar 124 includes a cutout portion 126 in the area of thecollar underlying the patient's chin. Cutout potion 126 provides acavity that receives the chin and/or jaw when the collar is positionedon the patient so that the collar is comfortable to the patient.

[0072] While collar 34 in FIG. 1 and collar 124 in FIG. 9 are bothillustrated as having a generally circular shape with a uniform heightand thickness around the circumference (except for the chin cutout inFIG. 9), it is to be understood that other variations in the structureof the collar are contemplated by the present invention. For example,the height and thickness of the collar can be reduced at the back of thepatient's neck because this portion of the collar does not directlysupport the coil in the collar. In addition, the collar can be made froma continuous piece of material that slips over the patient's head withan elastic portion to ensure that the collar remains properly positionedon the patient. Alternatively, the collar can be a strip of materialhaving ends that selectively secure to one another to attach the collarabout the patient's neck. In which case, any conventional fasteningdevice, such as snaps, clasps, hooks, a zipper, a button or VELCRO™, canbe used to attach the ends of the collar to one another.

[0073] It is important that the collar be properly positioned on thepatient. To that end, collar 124 in FIG. 9 includes markings 128 on anexposed surface thereof to assist in properly positioning the collar onthe patient. In the illustrated embodiment, collar 124 includes an arrow128 that indicates the central axis of the coil configuration, such ascentral axis 130 in FIG. 8A, which is the axis of symmetry for the coilconfiguration. To properly position the coil relative to the muscles tobe stimulated, the user aligns arrow 128 directly below the chin alongthe centerline of the face. It is to be understood that other indicia orindexing markings or mechanisms can be employed to position the collaron the neck at the proper location. For example, markings on the collarcould be provided on the portions of the collar that overlie the carotidarteries when the collar is positioned on the patient. The location ofthe carotid arteries are relatively easy to locate, either by the useror another person applying the collar and, thus, are useful inpositioning the collar merely by aligning the carotid artery markings onthe collar with the patient's carotid arteries.

[0074]FIG. 10 is a schematic diagram of magnetic stimulator 30. In theillustrated embodiment, collar 34 includes a snore sensor 130, such assensor 58 of FIG. 3, and circuitry for amplifying and filtering theanalog signal output by the sensor. Filtering is done to eliminateextraneous noise from the signal output from the snore sensor. Theamplified and filtered snore sensor signal is provided to sample andhold sensor 132, A/D converter 134 and microprocessor 136 in controlunit 32. Microprocessor 136 controls the operation of a coil drivecircuit 140, which provides energy to coil 142 in collar 34. Memory 138stores threshold data, data provided from microprocessor 136, andprograms carried out by the microprocessor. Power from a power supply144 is provided to coil drive circuit 140 through an over currentprotection circuit 146. Power supply 144 can be any suitable powersupply that is capable of providing sufficient power to coil 142. Coildrive circuit 146 can be any suitable circuit for energizing coil 142,such as a selectively dischargeable capacitance. Over current protectioncircuit 146 can be any suitable circuit that limits the amount of energy(voltage/current) that can be provided to coil 142 for safety purposes.

[0075] The energy limiting function of over current protection circuit146 is separate from the energy level setting function of microprocessor136. More specifically, over current protection circuit 146 ensures thatthe patient is never stimulated at a level that is above thatappropriate for that patient, even if the maximum stimulation intensitylevel is set by the user. Preferably, the maximum current permitted byover protection circuit 146 is set in advanced based on thecharacteristics of the patient using the stimulator.

[0076] One embodiment of the operation of magnetic stimulator 30 isdiscussed below with reference to FIG. 11, which is a flowchartillustrating a process carried by the magnetic stimulator in achievingits therapeutic effect. More specifically, the process illustrated inFIG. 11 is repeatedly conducted under the control of the microprocessoronce the magnetic stimulator is activated. In step S30, the airway soundvibrations are detected using an appropriate transducer that is incommunication with the patient's airway, such as audio snore sensor 58of FIG. 3. These sound vibrations are output by the transducer as anelectrical signal, which is bandpass filtered, amplified and convertedfrom an analog to a digital signal S in step S32. Filtering is performedto eliminate noise in the signal output from the sensor, andamplification is performed to adjust the signal level to a levelsuitable for the components receiving that signal. Signal S is providedto microprocessor 136.

[0077] In step S34, the magnitude of signal S is compared to a thresholdmagnitude S_(TH), which is a predetermined minimum noise threshold.Threshold magnitude S_(TH) is preferably determined and set so inadvance so that it is specific to the patient using the magneticstimulator. If signal S does not exceed S_(TH), the signal output by thetransducer is considered to not correspond to a snore and the processreturns to step S30. If signal S exceeds S_(TH), the signal isconsidered to correspond to a snore sound and is integrated in step S36to determine its duration S_(D) and energy level S_(E), which are storedin memory 138.

[0078] In step S38, duration and energy level thresholds D_(TH) andE_(TH), respectively, are set. These thresholds can have fixed valuesthat are determined and set in advance, preferably based on thecondition of the patient, or they can have values that vary during theoperation of the stimulator. For example, the magnitude of duration andenergy level thresholds D_(TH) and E_(TH) can be set based on the recenthistory of snore sounds. During an intense snoring period, the energylevel thresholds D_(TH) and E_(TH) can be increased so that loweramplitude snore sounds. On the other hand, these threshold values can bedecreased, thereby increasing the sensitivity of the stimulator, ifapnea events are detected or if the intensity (magnitude and/orduration) of the snore sounds diminish.

[0079] In a preferred embodiment of the present invention, an average ofa predetermined number of previous signals corresponding to snore soundsare used to set thresholds D_(TH) and E_(TH). For example, the durationand energy level of the past ten snore sound signals, eliminating themaximum and minimum values, can be averaged to set these thresholds. Itis to be understood, however, that other techniques can be used toaverage the previous snore sounds signals to set D_(TH) and E_(TH).

[0080] In steps S40 and S42, the duration S_(D) of the snore soundsignal is compared to duration threshold D_(TH), and the energy levelS_(E) of the snore sound signal is compared to energy level thresholdE_(TH). If either of these thresholds are not met, the process returnsto step S30, meaning that the snoring sound does not qualify as anapneic event. If, however, both of these thresholds are met, the snoresound signal is considered to qualify to an apneic event and the processcontinues to step S44.

[0081] In step S44, microprocessor determines if more than 30 secondshave elapsed since the last snore sound signal S qualifying as an apneicevent. If it has been 30 seconds or less since the last snore soundsignal S qualifying as an apneic event, a counter in microprocessor 136is incremented in step S46. Thus, the counter is incremented if theupper airway sound producing a sound signal that qualifies as an apneicevent is detected at or within 30 seconds of a previous sound signalalso qualifying as an apneic event. If more than 30 seconds haveelapsed, this counter is reset in step S48 and the process returns tostep 30.

[0082] In step S50, the microprocessor determines if the counter hasreached three. If not, the process returns to step S30. If so, themicroprocessor determines, in step S52, if more than 60 seconds haveelapsed since the previous stimulation. If only 60 or less seconds haveelapsed since the previous stimulation, the process returns to step S30.If, however, more than 60 seconds have elapsed, the stimulation level isset by the microprocessor in step S54 and the microprocessor causes coildrive circuit 140 to apply energy to the coil to stimulate the patientat the set stimulation level.

[0083] The initial stimulation level is typically set in advance by aqualified physician. However, an input device, such as dial or keypad,on or operatively coupled to the control unit can be used to adjust thislevel. Preferably, a lockout mechanism is provided to prevent the userfrom adjusting the intensity level beyond that specified by thephysician. For example, the control unit can be preprogrammed, prior tobeing provided to the user, to not accept or apply any stimulationlevels above a predetermined level. Thus providing a further safeguardagainst excessive stimulation.

[0084] The present invention also contemplates modifying the intensityof the magnetic stimulation as necessary during the stimulation therapy.This is done in step S56 following the application of the magneticstimulation using a feedback system. For example, as additional upperairway sounds qualify as snore sounds or further qualify as an apneicevents, the intensity of the magnetic stimulation can be increased,preferably incrementally, to further stabilize the airway. Theincremental amount of each increase can be fixed or variable, and eachincrease need not be by the same amount. The amount of the incrementalincrease is typically established in advance or it can be set based onthe conditions of the patient, such as the snoring activity. In apreferred embodiment of the present invention, steps S30 through S50 arerepeated, and if the counter has reached three in step S50, thestimulation level is increased by a predetermined amount.

[0085] The stimulation level can also be decreased if the number ofupper airway sounds qualifying as snore sounds or further qualifying asapneic events decreases following the onset of stimulation. In thismanner, only the stimulation intensities necessary to treat the apneicevents are applied to the patient, thereby conserving power andminimizing use of the magnetic stimulator.

[0086] In a preferred embodiment of the present invention, if no apneicevent snore sounds are detected after 5 minutes after the onset ofstimulation, the stimulation level is reduced by a first predeterminedamount, which can either be fixed or variable. In a second embodiment ofthe present invention, steps S30 through S50 are repeated and if thecounter does not reach three in step S50, the stimulation intensity isreduced by the first predetermined amount. In both of these embodiments,the stimulation intensity can be further reduced by a secondpredetermined amount for each consecutive time period, such as a 5minute interval, during which no apneic events are detected until thestimulation level reaches zero. This second predetermined amount can bethe same as the first predetermined amount and can be fixed or variable.Thereafter, the process returns to step S30.

[0087] It is to be understood, that the time period during which furtherapneic events are monitored to determine how to change (or cease) thestimulation level, if necessary, can be a fixed or variable length oftime. Also, the present invention contemplates simply ceasingstimulation after a predetermined period of time has elapsed duringwhich a minimum number, e.g., zero, of apneic events are detected. It isto be further understood that this same scenario for decreasing theintensity of the magnetic stimulation can also be used to increase itsintensity.

[0088] While the occurrence of an apneic event is detected in step S50if the counter reaches three, it is to be understood that other integernumbers of sounds qualifying as a snore sound can be used as a benchmarkfor determining the occurrence of an apneic event. For example, two orfour snore sounds occurring within a predetermined time period can beused to determine the occurrence of an apneic event. Furthermore, theduration of this predetermined time period, which corresponds to the 30sec period in step S44, can be set in advance or it can be variablebased on the monitored conditions of the patient.

[0089] Although the initiation, modification and termination ofstimulation can be conducted using the process discussed above, it isalso possible to apply the process discussed in U.S. Pat. No. 5,203,343,the contents of which are incorporated herein by reference, to themagnetic stimulator. The process illustrated in the '343 patent isintended for use with a positive airway pressure device to control theinitiation, modification and termination of the positive airwaypressure. However, the process taught by the '343 patent can be used inan analogous manner to control the magnetic stimulator. In which case,it is not the pressure level that is controlled, but the intensity ofthe magnetic stimulation.

[0090] The initiation, modification and termination of stimulation canalso be performed based on the patient's respiratory cycle. For example,stimulation can be synchronized with the patient's inspiration so thatstimulation begins at the same time as inspiration. Alternatively,stimulation can be initiated just prior to, i.e., not more than onesecond before, or just after, i.e., not more than one second after, theinitiation of inspiration. This method obviates the need to determinethe occurrence of snore and/or an apneic event and attempts to eliminatesuch events before they occur.

[0091] In an exemplary embodiment of the present invention, stimulationenergy is provided to the patient by energizing the coil with a seriesof current pulses, each pulse having a prescribed magnitude andduration. The magnitude of the pulses in the pulse train and/or the dutyratio can be set to determined the overall intensity of the stimulationprovided to the patient. For example, in a preferred embodiment, aseries of pulse trains, each having a pulse rate between 5-30 pulses/secand lasting between 1-3 seconds, is provided to the patient.Alternatively, stimulation can be provided in phase with the patient'sinspiratory effort. This requires monitoring the inhalation andexhalation of the patient using any appropriate device and timing thestimulation to coincide with the onset of inhalation. It is to beunderstood, however, that stimulation can be initiated at any periodoffset from the onset of inspiration so that the initiation ofstimulation either precedes or follows the onset of inspiration.

[0092] Maximum magnitudes and pulse repetition rates can be set inadvance to limit the overall stimulation that the patient receives.Typically, these magnitudes and pulse repetition rates, as well as theduration of the pulse trains, threshold levels and other variablesdiscussed above are set by a doctor or other physician after conductingan evaluation of the patient. Furthermore, the current pulses areoptimized to reduce the energy dissipated in the coil. For example, thecoil is energized by a current emanating from charge stored on alow-loss capacitor, most of which charge is recaptured during theapplied pulse.

[0093] Although not shown in the process illustrated in FIG. 11, theoverall energy level provided to the coil can be ceased or reduced ifthe coil temperature exceeds a predetermined value. Conversely, theenergy level can be increased so long as the coil temperature remainswithin an acceptable range. This feature of the present inventionensures that the patient's safety is not compromised while stillproviding the maximum therapy to the patient.

[0094] The present invention further contemplates controlling theapplication, changes in intensity, and cessation of stimulation based onother criteria. For example, the present invention contemplates delayingthe application of stimulation energy to the patient after the magneticstimulation system has been activated, so that the patient has theopportunity to fall asleep prior to the start of the stimulationtherapy. This can be accomplished, for example, by causing a timer to beactivated, either manually or automatically upon activation of thestimulation system, and once the time counts out a predetermined timeinterval, initiating the stimulation therapy. This therapy delay featurecan also be based on a conventional clock so that the user can set thetherapy to begin at any preselected time during the night. Similarly,the magnetic stimulation system of the present invention can ceaseapplication of the stimulation after the passage of a selectable timeperiod so that stimulation ceases before the patient typically awakes,thereby preventing the user from being awaken by the stimulationtherapy. This delay in turning off the stimulation therapy can be basedon a time interval or based on a conventional clock.

[0095] The present invention also contemplates controlling thestimulation energy applied to the patient in a variety of ways tomaximize patient comfort. For example, one embodiment of the presentinvention contemplates incrementally increasing the intensity of thestimulation energy being delivered to the patient following theactuation of the stimulation system. This increase can take place inplace of or after the delay period discussed above. Another embodimentof the present invention contemplates incrementally decreasing theintensity of the stimulation energy being delivered to the patient. Thisdecrease can take place in place of or before the delay in turning offthe stimulation therapy discussed above. The intensity of thestimulation can also be controlled based on the patient's sleep stages,assuming, of course, that the appropriate sensors and control systemsare provided to detect and classify the patient's sleep stages.

[0096] The present invention further contemplates providing variousmethods for interrupting the stimulation therapy. For example, a pausefunction that stops stimulation therapy can be initiated by the usereither by manually actuating an input device, such as a button, on thecontrol unit or remotely. The stimulation therapy can also beinterrupted automatically, if, for example, a malfunction is detected.Restart of the stimulation therapy can begin automatically, after theelapse of a fixed or selectable time period, for example, or by manuallyactuating the input device, i.e., again actuating the button or theremote control. Restart of the stimulation therapy can begin at thestimulation energy levels existing prior to the pause, at the initialenergy level, or at some other preselected level. In addition, the delayfunction and/or the incremental intensity functions can be institutedduring the restart so that the user again has the opportunity to fallasleep in the absence of any stimulation therapy.

[0097] The present invention also contemplates providing a safetyfeature in which a maximum stimulation energy that can be provided tothe patient is set. This can be accomplished via a control unit. Thisstimulation energy provided to the patient will not be exceed the setmaximum regardless of the stimulation energy set by the user on thecontrol unit. It is preferable that the means by which the maximumstimulation energy is set is secured so that it cannot be alteredinadvertently, or tampered with. The use of a password that must beinput in order to alter the maximum setting is an example of such asecurity feature.

[0098] In still another embodiment of the present invention, themagnetic stimulation system is provided with an automatic turn-on and/oran automatic turn-off feature. This provides the advantages ofsimplifying the operation of the system and conserving power, forexample. Sensors on the collar, for example, such as a temperaturesensor or galvanic type sensor can detect when the appliance is disposedon the patient. The output of these sensors are used to control theactuation and deactivation of the stimulation system of the applicationand cessation of the stimulation therapy.

[0099] With the growing popularity of managed healthcare, healthcareproviders are becoming more concerned that the patients actually use theprescribed therapy devices. To meet this concern, the present inventionmonitors patient compliance by storing information regarding the used ofmagnetic stimulator, such as the amount of time that the unit was turnedon and/or the amount of time that the coil has been energized.

[0100] In one embodiment discussed above, the coil is only energizedonce an apneic event is detected. In another embodiment, the coil isenergized in synchronization with the patient's respiratory cycle. Thus,the present invention makes it difficult for the patient to deceive thehealthcare provider as to the actual usage of the device, therebyproviding a relatively reliable and accurate indication of the actualusage of the magnetic stimulator.

[0101] Furthermore, because the stimulator is capable of communicatingwith external devices using a modem, for example, patient compliance canbe remotely monitored by the healthcare provider with little or nopatient involvement. This same remote patient compliance monitoringfeature also permits the healthcare provider to monitor the operatingstatus of the stimulator, for example, by causing the device to run adiagnostic routine and reports the results.

[0102]FIG. 12 illustrates a further embodiment of the present invention.In this embodiment, the structure for the magnetic stimulator, includingthe coil and control unit are the same as in the previous embodiments.In this embodiment, however, miniature implantable intramuscularstimulators 160 and 162 are provided in or near the patient's musclesthat are targeted for stimulation or near the nerves that contract suchmuscles. Because these devices are relatively small, they can beimplanted using a hypodermic, thereby minimizing the invasiveness of theimplantation surgery. Also, because these devices are not physicallyconnected to any other devices, they do not suffer the medicalconsequences associated with providing an electrode permanentlypenetrating the patient's skin, as is the case with many conventionalimplanted electrodes.

[0103] As shown in FIG. 13, intramuscular stimulators 160 and 162include a receiver coil 164 that communicates with coil 56 in thecollar, high capacitance electrodes 166, and a decoding network 168.Receiver coil 164 and high capacitance electrode 166 transfer themagnetic energy provided by the coil into electrical energy that isapplied directly to the muscle (or nerve) contacting the intramusculuarstimulator. This permits specific muscles to be targeted forstimulation, which is especially beneficial in situations where thetargeted muscle is recessed deeply beneath the patient's skin or is noteasily distinguishable from non-target muscles of nerves.

[0104] Decoding network 168 enables the control unit to distinguish andcontrol a selected intramuscular stimulator using, for example, an AM orFM signal. In this manner, intramuscular stimulator 160 can becontrolled, for example, to stimulate the geniohyoid muscle withoutcausing intramuscular stimulator 162 to stimulate the sternohyoidmuscle. Of course, other muscles can be target using other intramuscularstimulators and groups of muscles (or one muscle) can be stimulatedusing a plurality of intramuscular or stimulators implanted into thosemuscles (or that single muscle) all of which have the sameidentification for activation purposes. The stimulation intensities andthe timing at which the muscles are stimulated can be varied in the samemanner discussed above with respect to the many ways in which areas A-Dcan be stimulated. See FIG. 4. This is accomplished by selectivelyactuating the intramuscular stimulators either independently of oneanother or in synchronization and controlling the stimulation intensitylevel of each intramuscular stimulator, all of which is done by thecontrol unit.

[0105] The present invention also contemplates providing an implantablepassive probe that alters the magnetic field strength in the vicinity ofthe probe in addition to or in place of the active probes discussedabove. In a preferred embodiment of the present invention, the passiveprobe is a glass encapsulated strip of material having a high magneticpermeability, typically about 0.5 mm in length and 2 mm long, and curvedso that the strip can wrap, at least partially, around a nerve. Such adevice having a high magnetic permeability reduces the magnetic field atits exterior. Providing such a device near a nerve fiber enhancesmagnetic stimulation by creating an increase in the gradient of theelectric field along the nerve fiber. This electric field gradient isbelieved to be the mechanism by which the nerve fiber is stimulated.

[0106] From the forgoing, it can be appreciated that the presentinvention increases the tension in the muscles that stabilize the upperairway to prevent its collapse. It is non-painful and more tolerablethan skin/surface stimulation techniques. The device is non-invasive,and, therefore, safer than systems that stimulate the musculature withimplanted electrodes. For those patients for whom electrical stimulationof the muscles stabilizing the upper airway is planned, magneticstimulation may be useful in establishing the efficacy of the plannedtreatment. In this regard, the intensity of the magnetic stimulationapplied by the qualified caregiver can be larger than that possible inthe unit intended for home use. This enables the caregiver to determineif electrical stimulation, either induced by the present invention orusing conventional implanted electrodes, will produce the desiredtherapeutic benefit in that patient.

[0107] In the previous embodiments of the present invention, themagnetic stimulating system is the sole means for treating the patient'sbreathing disorder. It is to be understood, however, that the presentinvention contemplates using the magnetic stimulating system inconjunction with other techniques for treating breathing disorders. Forexample, one embodiment of the present invention contemplates using themagnetic stimulating system in conjunction with conventional electricalstimulation systems to target additional muscles or muscle groups forstimulation or supplement the stimulation provided by theelectrode-based muscle stimulator.

[0108] Another embodiment of the present invention contemplates usingthe magnetic stimulating system in conjunction with a conventionalpressure support system that applies positive air pressure at the mouthand/or nose of the patient to “splint” the airway. Even if magneticstimulation the muscles of the airway does not fully open the airway, itis believed that the induced muscle stimulation will reduce thepressures necessary to be provided by the pressure support system inorder to splint the airway and treat the breathing disorder. It is wellrecognized that the pressure needed to be provided to the patient by thepressure support device to treat the breathing disorder should be keptas low as possible.

[0109] The present invention contemplates that the magnetic stimulatingsystem of the present invention can be used in conjunction with most, ifnot all, conventional the pressure support systems. Such pressuresupport systems typically include a pressure generator 172 thatgenerates a gas flow, a conduit 173 that carries the gas flow to thepatient, and a patient interface device 174 that communicates theconduit with the patient's airway. See FIG. 14. Examples of pressuresupport devices that are used in conventional pressure support systemsinclude a CPAP (continuous positive airway pressure) device, bi-leveldevices, which provide variable levels of pressure support during thepatient's respiratory cycle, such as the Respironics BiPAP® devices,PAV® devices and PPAP devices. Examples of suitable patient interfacedevices include nasal masks, oral appliances, nasal/oral masks, fullface masks, hoods, nasal cannulas, trachea tube, and any other devicethat communications a gas flow with the patient's airway.

[0110] The present invention also contemplates using the magneticstimulator discussed above as a diagnosis device to assess thelikelihood that a subject suffers from OSA. It has been clinicallydetermined using standard electromyography techniques that the muscleactivity in the upper airway of awake patients suffering from OSA ishigher than in normal subjects. By measuring the compliance of thesubject in the awake state, both in the presence and in the absence ofmagnetic stimulation, it is possible to determine whether that subjectis likely to suffer from OSA. Compliance is determined by measuring thechange in the cross-sectional area, and hence the volume, of thepatient's upper airway while different positive pressures are applied tothe upper airway by means of a standard continuous positive airwaypressure (“CPAP”) device.

[0111] In patients likely to suffer from OSA, the difference in themeasured compliance with and without magnetic stimulation is less thanthe difference in the measured compliance with and without magneticstimulation in normal subjects. This is so because patients likely tosuffer from OSA tend to have abnormally high muscle activity in theirupper airway in the awake state. Thus, the application of magneticstimulation to the upper airway in the awake state has little effect intensing the upper airway muscles, resulting in little change incompliance. In normal patients, however, the application of magneticstimulation to the upper airway generally has a more significant impacton compliance because the magnetic stimulation tenses the otherwiserelaxed upper airway muscles. Thus, by measuring compliance, firstwithout magnetic stimulation to the upper airway muscles and then withsuch stimulation, it can be determined that the subject is likely tosuffer from OSA if there is relatively little change in compliance underthese two conditions.

[0112]FIG. 14 illustrates an example of a system 170 for diagnosing thelikelihood that a subject suffers from OSA using the magnetic stimulatordiscussed above. Diagnosis system 170 includes a CPAP device 172 forproviding continuous positive airway pressure to the patients airway viaa nosemask 174 or other suitable nose sealing member. Magneticstimulator 30 induces tension in the subjects upper airway muscles. Anacoustic transducer 176 measures the subject's compliance, i.e., thechange in the cross-sectional area, and hence the volume, of thepatient's upper airway. It to be understood that other devices formeasuring the subject's compliance, such as through magnetic resonanceimaging (MRI), are contemplated by the present invention. An acoustictransducer is used for this purpose in the illustrated embodimentbecause of its relative simplicity, ease of use and low cost. In theillustrated embodiment, CPAP device 172, acoustic transducer 176 andmagnetic stimulator 30 are all operated under the control of a computer178. Also, a monitor 180 and keyboard 182 are coupled to computer 178.

[0113] System 170 diagnoses the likelihood that the subject suffers fromobstructive sleep apnea by first measuring the compliance of the subjectto obtain a first compliance level using acoustic transducers 176. Thisis done in the absence of magnetic stimulation. Next, a magnetic fieldis applied to at least one muscle group associated with an upper airwayof the subject using magnetic stimulator 30. The compliance of thesubject is measured while the magnetic field is being applied to obtaina second compliance level. The first compliance level is compared to thesecond compliance level to determine the difference therebetween. Thesmaller the difference between the first and second compliance levels,the more likely the subject suffers from obstructive sleep apnea. In apreferred embodiment of the present invention, computer 178 makes thiscomparison and outputs an indication of the likelihood that the subjectsuffers from OSA.

[0114] Although the invention has been described in detail for thepurpose of illustration based on what is currently considered to be themost practical and preferred embodiments, it is to be understood thatsuch detail is solely for that purpose and that the invention is notlimited to the disclosed embodiments, but on the contrary, is intendedto cover modifications and equivalent arrangements that are within thespirit and scope of the appended claims.

What is claimed is:
 1. A muscle stimulator adapted to apply a magneticfield to at least one muscle group associated with an upper airway of apatient having a breathing disorder to induce tension in said musclegroup to treat said breathing disorder, said muscle stimulatorcomprising: a plurality of loops of electrical wire; a power supply thatselectively provides electrical power to said plurality of loops toproduce said magnetic field; a sensor adapted to monitor a physiologicalcharacteristic of a patient; a control unit that receives signals outputby said sensor and controls application of said electrical power fromsaid power supply to said plurality of loops of electrical wire basedthereon; and a positioning appliance adapted to secure said plurality ofloops of electrical wire to a patient at a position relative to said atleast one muscle group such that said magnetic field produced byapplying said electrical power to said plurality of loops of electricalwire induces tension in said at least one muscle group to treat saidbreathing disorder.
 2. The muscle stimulator of claim 1 , furthercomprising a temperature sensor disposed proximate to said plurality ofloops of electrical wire to sense a temperature of said loops.
 3. Themuscle stimulator of claim 2 , wherein said control unit preventsapplication of electrical power to said plurality of loops of electricalwire responsive to said temperature detected by said temperature sensorexceeding a predetermined threshold temperature.
 4. The musclestimulator of claim 1 , wherein said sensor is an audio sensor disposedon said positioning appliance and adapted to detect snoring soundsproduced by said patient and to output a signal indicative thereof. 5.The muscle stimulator of claim 1 , wherein said sensor detects acondition of a patient associated with respiration outputs a signalindicative thereof.
 6. The muscle stimulator of claim 1 , wherein saidplurality of loops of electrical wire are non-overlapping and arecarried by said positioning appliance such that a peripheral portion ofeach loop is adjacent a peripheral portion of another loop.
 7. Themuscle stimulator of claim 6 , wherein each loop in said plurality ofloops has more than one turn.
 8. The muscle stimulator of claim 7 ,wherein each loop generally a same number of turns and all loops areenergized from a common pair of terminals.
 9. The muscle stimulator ofclaim 8 , wherein said turns in each loop are arranged in a spiral, suchthat turns distal from a common central axis in each loop have a radiusthat is greater than turns proximate to said common central axis in thatsame loop.
 10. The muscle stimulator of claim 6 , wherein an outerperipheral portion of at least one of said loops, which is not adjacenta peripheral portion of another of said loops, is carried by saidpositioning appliance so as to be spaced further apart from said patientthan another portion of said at least one loop that is adjacent anotherone of said loops responsive to said positioning appliance attachingsaid plurality of loops to said patient, thereby minimizing an amount ofheat produced by said loops that reaches said patient.
 11. The musclestimulator of claim 6 , wherein said plurality of loops of electricalwire comprises four loops having a common terminal and configured suchthat applying electrical power to said common terminal produces fourareas where said magnetic fields are concentrated.
 12. The musclestimulator of claim 6 , wherein said plurality of loops of electricalwire comprises three loops configured such that applying electricalpower to said three loops produces two areas where said magnetic fieldsare concentrated.
 13. The muscle stimulator of claim 6 , wherein saidplurality of loops of electrical includes a first loop and a secondloop, said first loop being independent of said second loop so that thatsaid first loop is capable of being energized independently of saidsecond loop.
 14. The muscle stimulator of claim 1 , further comprising athermal insulating material disposed between said plurality of loopsfrom said patient.
 15. The muscle stimulator of claim 1 , wherein saidpositioning appliance is a selectively attachable collar adapted toencircle a neck of said patient and to be worn by said patient such thatsaid plurality of loops are positioned proximate to said neck between achin and a sternum.
 16. The muscle stimulator of claim 15 , wherein saidcollar includes markings on an exposed surface thereof to assist inproperly positioning said collar on said patient.
 17. The musclestimulator of claim 1 , wherein said control unit is operatively coupledto said positioning appliance and said sensor via a flexible cable forhardwire transmission of signals between said control unit and saidsensor and said coil carried by said positioning appliance.
 18. Themuscle stimulator of claim 1 , wherein said sensor is carried by saidpositioning appliance such that properly positioning said positioningappliance on said patient locates said loops in a position relative tosaid muscles to be stimulated and also locates said sensor at anappropriate position on said patient for collecting relevant data. 19.The muscle stimulator of claim 1 , wherein said control unit includesmeans for comparing said signal output by said sensor to a thresholdvalue indicative of an occurrence of an apneic event, said control unitcausing said power supply to supply electrical power to said pluralityof loops of electrical wire responsive to said signal exceeding saidthreshold value.
 20. The muscle stimulator of claim 19 , wherein saidcontrol unit further includes means for monitoring a number of timessaid signal exceeds said threshold values during a predetermined timeinterval, said control unit causing said power supply to provide saidelectrical energy to said plurality of loops responsive to said numberof times said signal exceeds said threshold values during saidpredetermined time interval being greater than a first predeterminednumber.
 21. The muscle stimulator of claim 20 , wherein said controlunit includes means for adjusting said threshold values.
 22. The musclestimulator of claim 1 , wherein said control unit includes means foradjusting an intensity of said magnetic field produced by said musclestimulator and a duration that said magnetic field is applied to saidpatient.
 23. The muscle stimulator of claim 22 , wherein said means foradjusting said intensity of said magnetic field adjusts said magnituderesponsive to signals provided by said sensor.
 24. The muscle stimulatorof claim 1 , wherein said plurality of loops of electrical wire aredefined by a continuous electrical wire.
 25. The muscle stimulator ofclaim 1 , further comprising a warning system that provides a warningsignal indicative of one of a condition of said patient and a conditionof said muscle stimulator.
 26. The muscle stimulator of claim 1 ,further comprising an implantable non-conductive member adapted toprovide an electric field discontinuity to enhance excitability of anerve proximate to said non-conductive member responsive to applicationof said magnetic field.
 27. The muscle stimulator of claim 1 , furthercomprising a miniature intramuscular stimulator adapted to be implantedin said patient, said miniature intramuscular stimulator transferringenergy contained in said magnetic field produced by said into electricalenergy that is adapted to be applied directly to said patient at a siteof said intramuscular stimulator.
 28. The muscle stimulator of claim 27, wherein said intramuscular stimulator includes a receiving coiladapted to receive signals from said coil, a decoding network thatenables said control unit to distinguish and control said intramuscularstimulator independently of other intramuscular stimulators, and anelectrode for applying electrical energy to a portion of said patientcontacting said electrode, said electrical energy being derived fromsaid magnetic field applied to said intramuscular stimulator.
 29. Themuscle stimulator of claim 27 , further comprising a first intramuscularstimulator and a second intramuscular stimulator, wherein said controlunit is capable of actuating said first intramuscular stimulatorindependent of said second intramuscular stimulator.
 30. A musclestimulator adapted to apply a magnetic field to at least one musclegroup associated with an upper airway of a patient having a breathingdisorder to induce tension in said muscle group to treat said breathingdisorder, said muscle stimulator comprising: a plurality of loops ofelectrical wire; means for supplying electrical power to said pluralityof loops of electrical wire to produce said magnetic field; means formonitoring a physiological characteristic of a patient; means, receivingsignals output by said first sensing means, for controlling saidelectrical power provided to said plurality of loops based thereon; andmeans for maintaining said plurality of loops of electrical wire at aposition relative to a patient so as to direct said magnetic fieldproduced by said plurality of loops at said at least one muscle group toinduce tension in said at least one muscle group to treat said breathingdisorder.
 31. A method of applying a magnetic field to at least onemuscle group associated with an upper airway of a patient having abreathing disorder induce tension in said muscle group to treat saidbreathing disorder, said muscle stimulator comprising: affixing aplurality of loops of electrical wire proximate to said at least onemuscle group; monitoring a physiological characteristic of a patient;providing electrical power to said plurality of loops of electrical wireto produce said magnetic field based on said monitored physiologicalcharacteristic, thereby inducing tension in said at least one musclegroup to treat said breathing disorder.
 32. The method of applying amagnetic field according to claim 31 , further comprising the steps:generating a signal indicative of said physiological characteristic;comparing said signal to a threshold value indicative of an occurrenceof breathing disorder; and applying electrical power to said pluralityof loops of electrical wire responsive to said signal exceeding saidthreshold value.
 33. The method of applying a magnetic field accordingto claim 32 , further comprising the step of monitoring a number oftimes said signal exceeds said threshold value during a predeterminedtime interval, and applying said electrical energy to said plurality ofloops responsive to said number of times said signal exceeds saidthreshold values during said predetermined time interval being greaterthan a first predetermined number.
 34. The method of applying a magneticfield according to claim 33 , further comprising the step of adjustingsaid threshold values.
 35. The method of applying a magnetic fieldaccording to claim 31 , further comprising the step of adjusting anintensity of said magnetic field and a duration that said magnetic fieldis applied to a patient.
 36. The method of applying a magnetic fieldaccording to claim 31 , further comprising providing a non-conductivemember proximate to a nerve in a patient, said non-conductive memberproviding an electric field discontinuity to enhance excitability ofsaid nerve responsive to application of said magnetic field.
 37. Asystem for diagnosing the likelihood that a subject suffers fromobstructive sleep apnea, comprising: a compliance measuring systemadapted to measure a compliance level of said subject; a magneticstimulator adapted to magnetically stimulate at least one muscle groupassociated with an upper airway of said subject; means for causing saidcompliance measuring system to measure a first compliance level of saidsubject in an absence of magnetic stimulation and to measure a secondcompliance level of said subject while said magnetic stimulation isbeing applied to said least one muscle group associated with said upperairway; and means for comparing said first compliance level to saidsecond compliance level to determine a difference therebetween, wherebythe smaller said difference between said first and said secondcompliance level, the more likely said subject is likely to suffer fromobstructive sleep apnea.
 38. A method of diagnosing the likelihood thata subject suffers from obstructive sleep apnea, comprising the steps of:measuring a compliance of said subject to obtain a first compliancelevel; applying a magnetic field to at least one muscle group associatedwith an upper airway of said subject; measuring said compliance of saidsubject while applying said magnetic field to at least one muscle groupassociated with an upper airway to obtain a second compliance level; andcomparing said first compliance level to said second compliance level todetermine a difference therebetween, whereby the smaller the differencebetween said first and said second compliance level, the more likelysaid subject is likely to suffer from obstructive sleep apnea.